Signametrics Corporation SMU2060, Руководство оператора

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Figure 4-15. AC coupled timing measurements with Threshold DAC.
In Figure 4-15, the DMM is set to the 2.4 ACV range, while the input is a 10% duty-cycle wave with 5 V peak-to-
peak. Due to AC coupling, the input at the comparator is between –0.5 V to + 4.5 V. The Median Value is +2.0 V,
which would be the optimal Threshold value.
Figure 4-16. Comparator and Threshold DAC Settings
4.15.2 Using the Frequency counter
Both frequency and period measurements are available when the DMM is in ACV or ACI functions.
Frequencies between 2 Hz to 300 kHz can be measured. Use the
DMMReadFrequency .
DMMFrequencyStr DMMReadPeriod and DMMPeriodStr functions to read the frequency and
period. Following the execution of one of these functions, the frequency counter range is automatically
adjusted to optimize it for the measurement. It may take up to six measurements before the correct
frequency range is auto-selected. Once within range, the next frequency measurement is made at the last
selected range. Measurement time can vary from about 0.2s to 1s unless the Range lock feature is used.
For applications where frequency measurement speed is required, select the frequency range by using
DMMSetCounterRng . This function locks the frequency counter range to the ranges indicated in Fugyre
4,17, preventing it from auto-ranging. The benefit is that it makes it much faster by eliminating the time
necessary for the counter to range. A significant improvement in counter speed can be realized by
selecting a range lower than the signal frequency. The tradeoff in in counter resolution. For instance, to
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